MICROCHEMICAL REACTIONS OF THE COMMON ELEMENTS 301 



calcium with the barium, particularly if much ammonium chlor- 

 ide is present, or if much sodium acetate has been added to 

 mitigate the action of mineral acids. 



From mixtures, strontium may sometimes be precipitated in 

 an amorphous condition if the solution is quite concentrated, 

 and may thus interfere with the test. Pure salts of strontium 

 give, even in very concentrated solutions, only a granular deposit 

 consisting of globular masses, exhibiting no distinguishable 

 crystal form. 



Magnesium is precipitated from ammoniacal solutions, but 

 neither from acid nor from neutral solutions; hence the pres- 

 ence of this element will not mask the test for barium. 



In addition to calcium and strontium, there are a number of 

 other elements, which, if present, will either be precipitated in 

 insoluble form or will interfere with the formation of the barium 

 crystals. In this list the most frequently met with will be lead, 

 iron, zinc, rare earths and less often copper, mercury, uranium, 

 and titanium. 



EXPERIMENTS. 



a. Crystallize a little of the reagent K 4 Fe(CN) 6 , alone, and determine its optical 

 properties. 



b. Try reagent on pure salts of Ca, Sr, Ba, using both dilute and concentrated 

 solutions. Try again, this time proceeding as directed above, using HC 2 H 3 O 2 and 

 NH 4 C1. 



c. Try the reagent on mixtures of Ca and Sr, Ca and Ba, Sr and Ba. 



d. Try effect of the reagent on salts of Pb, Zn and Fe. Then make mixtures of 

 Ba and these elements and test. 



e. Make a preparation of K2BaFe(CN)e, measure the angles of the crystals and 

 determine the optical properties of the compound. 



Behavior with Ammonium or Potassium Bichromate. 



The reagent is applied to the test drop in solid form, Method 

 777, page 252. 



From acetic acid solution, barium chromate BaCr04 is im- 

 mediately precipitated, orthorhombic, in the form of minute 

 light-yellow globular masses, or tiny rods with rounded ends. 

 Strontium chromate will not separate from acid solutions but 

 only from -neutral or slightly alkaline solutions. Calcium is 



